Return a topological ordering of a graph

Q: Return a topological ordering of a graph

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Question

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Problem: Output a topological ordering

Given a directed graph with n nodes labeled 0..n-1 and a list of directed edges edges, return a topological ordering of the nodes.

A topological ordering is a permutation of all nodes such that for every directed edge (u, v), node u appears before node v in the ordering.

Input

Integer n
List edges where each element is a pair (u, v) meaning u -> v

Output

Return a list of length n containing one valid topological order.
If no topological order exists (graph contains a cycle), return an empty list (or explicitly signal failure).

Constraints (reasonable defaults)

1 <= n <= 2e5
0 <= |edges| <= 2e5

Follow-up

Explain how you would ensure the returned order is correctly produced (i.e., not just detecting that a topo sort exists, but actually outputting the sequence).